The present invention relates generally to an apparatus and method for packaging food items and more particularly to an apparatus and process for packaging and stacking food items in individual slices having heat tack seals.
Various methods and apparatus have been proposed and utilized for the manufacture and packaging of individual slices of food items such as cheese. Although the available apparatus and methods are suitable for the packaging of individual slices, they are not without disadvantages.
One distinct apparatus and method is disclosed in U.S. application Ser. No. 07/791,490, filed on Nov. 12, 1991, whose disclosure is incorporated herein by reference. In Ser. No. 07/791,490 the package for the individual slices is formed from a continuous film or web of a thermoplastic material. The web is first folded in V-folded condition. As used herein, the term V-folded condition refers to a length of material which has been folded over onto itself so as to form what may subsequently be identified as a front sheet and a rear sheet which are Joined by the fold at the bottom, so as to approximate the letter "V" in cross section. The web is typically folded such that the rear sheet is longer than the front sheet to define a flap section in the rear sheet, which extends beyond the top edge of the front sheet. The flap section is typically folded over onto the front sheet to form a tubular web.
For purposes of an example, the following description is given with processed cheese as the food item being wrapped. It will be appreciated that other items are within the scope of the invention. The food item, such as processed cheese, is inserted into the tube. The web and cheese are then flattened. Subsequently, cross-seals are formed transverse to the longitudinal length of the tubular web at predetermined intervals thus forming slices which are joined together. After the tube is cross-sealed it is severed along the cross-seals in order to produce individually wrapped slices of cheese.
Several processes presently exist for providing the cross-seal. In one commonly used method, the transverse cross-seals are formed by subjecting the flattened web (with the inserted hot cheese) to pressure, at the desired locations. The pressure is applied such that an ultra-thin layer or film of cheese is left in the transverse sealing section. The ultra-thin layer or film of cheese acts as an adhesive to hold the two layers of the plastic web together. After this "cheese seal" has been formed, the web is severed at the sealed sections to define individual slices of cheese.
Although the "cheese seal" provides an adequate seal for the individual slices of cheese, the shelf life of the cheese product after it is packaged is not as long as would be desirable. This is due to the face that the cheese seal is a relatively weak seal which will eventually deteriorate and which allows air to enter into the slices under ordinary atmospheric conditions. The slices thus will soon dry out or spoil, particularly near the edges where the "cheese seal" is formed.
Other methods of providing a transverse cross-seal have also been disclosed. For example, U.S. Pat. No. 4,586,317 (Bussell), whose disclosure is incorporated herein by reference, discloses an arrangement for forming a seal in packaging material (such as processed cheese) which utilizes a sealing element having a finite number of small channels in the surface. The packaging film is co-extruded or laminated to include an inner sealing layer of relatively low thermal plastic melt temperature and an outer layer which does not melt under sealing conditions. The tube is heated and compressed transversely by the sealing elements thereby sealing the internal layers of the packaging film together. Such a sealing method is also employed in the arrangement disclosed in WO 91/02461 (Davison et al.) whose disclosure is incorporated herein by reference. Although the apparatus and method disclosed in this patent provide a suitable cross-seal, the finished product suffers from the same disadvantages that are described above. Since the longitudinal seal is formed by providing a flap in the V-folded condition web and simply overlapping the flap with the upper surface of the front sheet of the web, a poor seal is formed. Thus, air and other atmospheric products will enter into the wrapped slices of cheese, reducing the shelf life of the product.
Another sealing device is available from Kusther Industries S.A. The Kustner device employs two pairs of opposing rotating cylinders wherein at least one of the opposing cylinders has heated cleats attached thereto. Seals are formed by having a flattened cheese product tube having hot cheese therein move through one of the pair of opposed cylinders and being pressed by the heated cleats on the opposed cylinders. The heated cleats are aligned where the tube passes through the opposed cylinders. The tube is then conveyed to another pair of opposed cylinders having heated cleats and the process is repeated so as to form seals where the tube is pressed. It should be noted that the Kustner device only heats the seals when the cleats make contact with the seals and the dwell time of the seal on the cleats is approximately 0.01 seconds.
One solution to the problems present in the prior art is disclosed in U.S. application Ser. No. 07/791,490, whose disclosure is incorporated herein by reference. Ser. No. 07/791,490 teaches to provide an individual slice of cheese which is wrapped in a package which is hermetically sealed on all sides. To accomplish this, a hermetic seal is formed along the longitudinal edge of the web as well as along the transverse cross-seals. A hermetically sealed package would have several advantages. For example, a hermetically sealed slice would permit immersion for cooling and sanitizing. Further, a hermetically sealed slice is essential to aseptic packaging.
Despite the advantages of using hermetically sealed slices, the present invention provides other advantages. For example, the hermetically sealed slices are harder to open than other seals and a hermetic seal may not always be necessary.
Therefore, in view of the above, it is an object of the present invention to provide an apparatus and a method for producing individual slices of food items, such as processed cheese, which avoid the disadvantages of a "cheese seal" and provide an alternative to hermetically sealed packaging. In other words, the present invention involves producing a sealed packaged slice having the positive attributes of a "cheese seal" (i.e. easy to open and inexpensive) and a hermetically sealed slice (i.e- strong bond and long preserving time).
It is a further object of the present invention to provide an apparatus and method for providing a continuous and efficient arrangement for forming a longitudinal heat seal along the face of the folded packaging web.
It is a further object of the present invention to provide an apparatus which can form heat seals in an inexpensive manner by allowing present packaging devices, such as hot-fill machines, to be retrofitted with a crimp/sealing station which produces heat seals which are better than "cheese seals".